Field of the Invention
The present invention relates to a silicon target for sputtering film formation and a method for forming a silicon-containing thin film.
Description of the Related Art
Silicon-containing thin films such as a silicon film, a silicon oxide film, a silicon nitride film, and a silicon nitride-oxide film are used in various fields. For example, the silicon-containing thin films are used as an insulator film and a dielectric film in the field of semiconductor devices, as an antireflective film in the field of optical materials, or as a light-shielding film and a phase-shifting film in the field of photomask technology.
A sputtering method using a silicon-containing target material has been widely used to form the silicon-containing thin films for reasons that the method can be performed at low cost, there are relatively few material restrictions therein, and the method is highly controllable.
The silicon-containing target material is generally attached to a metallic backing plate via a conductive bonding material such as indium and tin. A voltage is applied to the backing plate, and the voltage passes through the bonding material to the silicon target material. Heat is thereby generated due to electric resistance. Thus, oxygen-free copper or the like having excellent cooling efficiency and conductivity is generally used for the backing plate.
A silicon target material is a typical silicon-containing target material. To improve wettability with the bonding material, an “adhesive layer” of copper, chromium, nickel or the like having a thickness of about 1 to 10 μm is preferably provided on a bonding surface of the target material (Japanese Patent Laid-Open No. 07-268616).
When the target material has high electric resistance, abnormal electrical discharge such as arc discharge may occur during sputtering. Thus, the target material preferably has low electric resistance. There has been proposed a silicon target material whose resistance is lowered by adding a dopant such as boron (Japanese Patent Laid-Open No. 2003-322955).
The present inventors conducted an experiment on forming a silicon compound thin film for use as a light-shielding film or a phase-shifting film on photomask blanks by using a silicon target material whose resistance is lowered by adding a dopant and whose conductive type is n-type, and confirmed a phenomenon that a more amount of dust is generated therein in comparison with a target material made of a transition metal material or the like.
The inventors also confirmed that the amount of dust generated when the n-type silicon target material is used is not reduced even when an electric resistivity is lowered by increasing an amount of donor added to the silicon target material. The generated dust causes a defect in the formed silicon-containing thin film, and thereby deteriorates the film quality.
The present invention has been made to solve the above problems, and it is an object of the present invention to provide a silicon target for sputtering film formation which enables formation of a high-quality silicon-containing thin film by inhibiting dust generation during sputtering film formation.